Thanks in advance for the advice.

I have multiple items for sale and a buyer made an offer for one item for the exact price it was listed for  ($150) and then contacted me about pickup details. He then enquired about another of my items, one that was twice the price of the first and made an offer of $200 when it was listed for $300.

I declined the offer and explained that I needed at least $275 for the second item. He then messaged and asked what my lowest price would be and said he would not pay for the first item if I did not offer the second for a much reduced price. 

That's not okay, surely? Is there anything I can do about that sort of behaviour?